Recently the research of organic and polymeric electro-optic (EO) materials has made tremendous progress. EO coefficients (r33 values) of greater than 300 pm/V have been demonstrated through controlled molecular self-assembly and lattice hardening. These material properties have been further translated into very low half-wave voltage (Vπ) in Mach-Zender and phase modulators. In addition to their applications in photonic devices, organic EO materials offer great potential for integrating with nanotechnologies for new generation of photonic systems with much smaller size and lower power consumption.
To achieve ultrahigh EO activity, one of the key components in these newly developed organic EO materials is the conjugated (4-dialkylamino)-phenyltetraene bridge with terminal substituted CF3-TCF acceptors. This is a primary class of high-μβ chromophores with certain degree of synthetic efficacy. For general uses, it is critical to improve chemical stability and maintain all-trans conformation of these phenyltetraene-based chromophores to optimize their nonlinear optical (NLO) properties.
Recently, 2-alkyl-isophorone-embedded phenyltetraene chromophores have been developed (See FIG. 1, comparing AJL24-type chromophores where R is alkyl with AJL6-type chromophores where R is hydrogen). The alkylation sterically rigidified the polyenic bridge to ensure its all-trans conformation, and the end of the alkyl groups can be further functionalized with dendrons to provide shape modification. In a guest-host polymer containing one such chromophore, a very large r33 value of 262 pm/V at 1.31 μm has been demonstrated. However, this approach has its own design challenges. In an attempt to incorporate this type of chromophores into Diels-Alder (DA) crosslinkable polymers for better temporal stability, considerable decrease in EO activity has been observed. Spectroscopic studies on these new systems revealed that these chromophores tend to react with dienophiles such as maleimides through cycloaddition, which leads to decomposition of chromophores and interference of DA lattice hardening.
In general, a diene can only react with a dienophile in its s-cis conformation through the overlapped p-orbital. The above result revealed that a relatively high diene reactivity exist in these all-trans phenyltetraene-based compounds. This is not unusual because the s-trans conformers rotate through their σ-bonds easily to form s-cis conformers.
To address the problem, an understanding of the conformational rigidity of the methine skeleton is essential, as well as an understanding of how the skeleton conformation can be adjusted by the substitution at the R position (see FIG. 1). The present invention seeks to fulfill these needs and provides further related advantages.